The present invention relates to the implementation of wireless systems in a local telephone loop environment in what is usually called a Wireless Local Loop (WLL). The present invention particularly addresses the air interface and protocols used in the implementation of a Wireless Local Loop.
The local loop of a telephone system is what some have termed the xe2x80x9clast milexe2x80x9d or the xe2x80x9clast 1000 feetxe2x80x9d. This local loop is essentially the copper wire that connects the customer premises (i.e., a house or business) to the telecommunications network. The cost of laying down the copper wire can be very expensive (ie, over $1 per foot). Where communities are rural in nature as in some parts of the United States or in developing countries, laying down such an infrastructure can be prohibitively expensive.
As an alternative to installing a wire or cable infrastructure, these rural communities are turning to wireless solutions for their telecommunication needs. However, conventional wireless telecommunication technologies suffer from a number of disadvantages. Often times, because of the quality of the service, modem connections are frequently difficult to establish and maintain. Even where modem connections are possible, data rates are often prohibitively slow.
A further disadvantage of conventional wireless telecommunication technologies relate to their inefficient use of their RF spectrum resources. Subscribers transferring data over the network occupy channels that would otherwise be available for voice communication. In instances in which many subscribers are, for example, accessing the internet, these conventional wireless technologies suffer from a serious degradation in Grade of Service (GOS) resulting in an increase in the percentage of calls blocked (i.e., Erlang B).
These deficiencies are particularly troublesome in view of the fact that data usage is bursty in nature. Analysis of internet data usage indicates that approximately 95-97% of the time, the data network is idle. Furthermore, the aggregate throughput to a user is typically less than 5 kilobits per second.
Therefore, there is a need for a wireless telecommunication system to replace the local loop which more efficiently allocates resources between voice and data communications yet maintains a desirable high GOS.
The following U.S. Patents are made of record for teaching various aspects of wireless telecommunications.
In U.S. Pat. No. 5,239,673, issued Aug. 24, 1993, entitled xe2x80x9cScheduling methods for efficient frequency reuse in a multi-cell wireless network served by a wired local area network,xe2x80x9d Natarajan describes communication methodologies that realize an efficient scheduling and frequency reuse in a wireless communications network that is served in a wired network.
In U.S. Pat. No. 4,639,914, issued Jan. 27, 1987, entitled xe2x80x9cWireless PBX/LAN system with Optimum Combining,xe2x80x9d Winters discloses a wireless LAN system that employs adaptive signal processing to dynamically reassign a user from one channel to another.
In U.S. Pat. No. 4,837,858, issued Jun. 6, 1989, entitled xe2x80x9cSubscriber Unit for a Trunked Voice/Data Communication System,xe2x80x9d Ablay et al. disclose a trunked voice/data subscriber that operates in either a voice mode or one of three data modes.
In U.S. Pat. No. 4,852,122, issued Jul. 25, 1989, entitled xe2x80x9cModem Suited for Wireless Communication Channel Use,xe2x80x9d Nelson et al. disclose a wireless communication system and, specifically, a modem that communicates digital data with data terminal equipment.
In U.S. Pat. No. 5,603,095, issued Feb. 11, 1997, entitled xe2x80x9cRadio System and a Subscriber Terminal for a Radio System,xe2x80x9d Uola discloses a wireless local loop system having at least one exchange, at least one subscriber database and base stations, and subscriber terminals communicating with the fixed network via a radio path.
In U.S. Pat. No. 5,555,258, issued Sep. 10, 1996, entitled xe2x80x9cHome Personal Communication System,xe2x80x9d Snelling et al. disclose a wireless, in-house telephone system designed to provide multi-line telephone operations, allowing the consumer to set up a multiple telephone, multiple line system without having to use wired phone connections running throughout the building.
In U.S. Pat. No. 5,689,511, issued Nov. 18, 1997, entitled xe2x80x9cData Receiver for Receiving Code Signals Having a Variable Data Rate,xe2x80x9d Shimazaki et al. disclose a data receiver capable of identifying the code rate of received data and decoding the data at an adequate rate without resorting to a data buffer or a plurality of decoding circuits.
In U.S. Pat. No. 5,504,773, issued Apr. 2, 1996, entitled xe2x80x9cMethod and Apparatus for the Formatting of Data for Transmission,xe2x80x9d Padovani et al. describe a data format which facilitates the communication of various types of data, and data of various rates, to be communicated in a structured form.
In U.S. Pat. No. 5,511,067, issued Apr. 23, 1996, entitled xe2x80x9cLayered Channel Element in a Base Station Modem for a CDMA Cellular Communication System,xe2x80x9d Miller describes a layered channel software element which supervises the operation of channel element modem resources in a CDMA cellular telephone system that includes forward channels for conveying message and signalling data from a CDMA system base station to mobile units and,reverse channels for conveying message and signalling data from mobile units to base stations.
Wireless local area networks (WLAN) have been available for connecting various computers in a local area. However, such systems have not been appropriate for application on the scale of a local loop. The method of transmitting and receiving signals in WLAN""s is not appropriate for the large distances and varied weather conditions encountered in a local loop scenario. Wireless local area networks have the further disadvantage that they cannot carry voice information appropriate for a telephone system.
It is an object of the invention to provide a wireless telecommunication system that allows individual subscribers in an area of service seamless telecommunications access (i.e., POTS (plain old telephone system), ISDN (Integrated Services Digital Network), data, multimedia, etc.) to a telecommunications network. This system facilitates full voice, data, and fax utilization. This system is designed to replace existing local loops or provide infrastructure for those communities in which no local loop is in place.
These and other objects are achieved by a wireless local loop (WLL) comprising a first interface connecting the WLL to the telecommunications network, a second interface connecting the WLL to a plurality of customer premise equipment (CPE) such as telephones, faxes, and computers, and point to multi-point radio frequency (RF) communications channels connecting the first interface to the second interface. The multi-point RF communication channels provide the user with traffic/bearer data, user control data and radio link specific overhead and control. Traffic bearer data may include the user""s encoded voice or data signal. User control data may include ISDN (Integrated Services Digital Controller) D-channel, translated CAS (Channel Associated Signaling) or OAMandP (Operations, Administration, Maintenance and Performance). Radio link overhead and control may include power settings, timing and framing. The present invention makes improvements to the WLL system while not requiring substantial changes to the telecommunications network or the customer premise interface (CPI).
It is a further object of the present invention to is provide concentrated access to the telecommunications network to buildings, campuses, or similar organizations in the area of service that are expected to have high telecommunications traffic demand. This and other objects of the invention are achieved by a capability referred to as xe2x80x9cembedded concentrated accessxe2x80x9d which allows the removal of a specified number of channels from the pool of multi-point RF communication channels and assigns them to the high traffic demand structure. These removed channels are referred to as the xe2x80x9cmicro-channel bank.xe2x80x9d The micro-channel bank provides the high traffic demand structure with traffic/bearer data, user control data and radio link specific overhead and control. The micro-channel bank is assigned to an extended radio unit (ERU) attached to or associated with the high traffic demand structure. The ERU provides traffic messaging and bearer channels to a micro-channel bank via the digital radio link (DRL). The remaining multi-point RF communication channels provide an acceptable grade of service (GOS) to the other subscribers in the area of service.
It is a further object of the present invention to provide for dynamic pool sizing of the various channels in the WLL. As the usage conditions of the WLL change, the size of the various pools of channels can be dynamically changed to meet the differing conditions. Such dynamic pool sizing can be used upon system initialization to get all the subscriber units on the system operational as quickly as possible. Dynamic pool sizing can also be used to improve overall system performance during adverse weather conditions so as to increase the processing gain of the system.
It is a further object of the present invention to provide the subscriber with a fast and efficient wireless data interface. This and other objects of the present invention are achieved by a capability referred to as xe2x80x9cembedded data access.xe2x80x9d The present invention advantageously uses subscriber usage statistics (data usage is idle approximately 97% of the time) to allow a large group of subscribers shared access to a smaller pool of RF traffic channels. The system performs at a grade of service (typically 1% in the United States) related to percentage of calls blocked (i.e. Erlang B). The management of N subscribers in a smaller pool on M available channels is called xe2x80x9cconcentrationxe2x80x9d or xe2x80x9ctrunkingxe2x80x9d with a concentration ratio of N/M greater than 1. Concentration is one further aspect of the present invention.
Through the use of an interface at the subscriber premises, a direct data access protocol can be utilized to provide the subscriber with a fast and efficient wireless data interface. Such an interface would not use consumer-type modems to achieve such data communications. This would eliminate the requirement that each user be assigned one particular channel. Rather, several data users could use one data channel while still achieving similar or better performance as compared to a high-speed modem.